Method for pyrolyzing polyfluoroalkanes



Patented Aug. 30, 1949 2,430,500 METHOD FOR rraohrzmo POLYFLUOBO- ALKANFrederick B. Downing, Barney's loint, and Anthony F. Benning and RobertC. Mclhrness, Woodstown, N. J., assignors to Kinetic Chemicals, Inc.,Wilmington, Dei., a corporation of Delaware No Drawing. ApplicationDecember 0, 1945, Serial No. 633,264

3 Claims.

This is a continuation-in-part of our earlier iiled applications SerialNo. 435,064, now Patent No. 2,387,247, and Serial No. 475,526 filedFebruary 11, 1043, now abandoned.

This invention relates to the preparation of organic fluorine compoundsby pyrolysis. By py olysis, we mean the transformation of a compoundinto another substance or other substances through the agency of heatalone. (Hurd, The Pyrolysis of Carbon Compounds, p. 9.) The term"pyrolysis used in this specification therefore will include not onlythe decomposition of compounds but also the making of more complexcompounds. In the applications identified as Benning et 111., Serial No.344,666, flied July 10, 1940, now Patent No. 2,365,516, and Banning,Serial No. 379,473, filed February 18, 1941, now Patent No. 2,343,252,are disclosed two processes involving a reaction between afluoro-hydrocarhon and HCI in the presence of a catalyst. Thosereactions may be described as additive, since their apparent course isthe addition of HCl to the olenne in the place of double bonds. Thesereactions were carried out at comparatively low temperatures, in mostcases below 350 C., because those temperatures were satisfactory andbecause observations of a limited number 01 experiments at highertemperatures showed the existence of what were thought to be undesirableside reactions. We have now discovered that the side reactions arepyrolytic and of a fundamentally different nature than HCl addition, andthat they and other reactions that occur at elevated temperatures can beput to valuable use.

It is an object of this invention to produce organic compounds bypyrolysis. Another object of the invention is to produce compounds whichare useful, by methods which are economically and technicallysatisfactory. Another object of the invention is to produce new fluorohydrocarbons. A particular object of the invention is to synthesizefluoroalkenes by the pyrolysis of polyfluoroalkanes. Another object ofthe invention is to produce the compound CH2=CF2 by methods which aretechnically and economically satisfactory.

According to our invention polyfluoroalkanes, which may otherwise becalled polyfluoro aliphatic compounds consisting of carbon, hydrogen andfluorine. are made into other compounds by pyrolysis. This reaction maybe carried out in isolation, or in the presence of a catalyst," by whichwe mean a substance that affects the result without combining with thereactants. Inert gases such as nitrogen and helium may be present asdiluents orbufl'ers" The fluoroalkanes, which may be pyrolyzed inaccordance with our invention, include i,1,1-trifluoroethane and itshomologs; 1,1-difluoroethane and its homologs; 1,1,2-triiiuoroethane andits homologs; 1.1.1.2-tetrafluoroethane and its homologs:1,1,22-tetrafluoroethane and its homologs. pentafluorethane and itshomoiogs; hexafluoroalkanes 01' 3 to 5 carbon atoms and otherfiuoroalkanes containing one or more CF5 groups with at least onehydrogen on a carbon adjacent to a Ci'a group.

The compounds of the formula H(CF-.)1.F wherein a is an integer of atleast 3, including H(CF-.-) 5F, may be prepared by fluorinatingcompounds of the formula H(CF:) Cl with SbFs in a closed vessel attemperatures of from about C. to about 250 C. as disclosed in the jointapplication of Anthony F. Benning and Joseph D. Park, Serial No.603,256, flied July 4, 945, now abandoned.

As a starting material we prefer to use a polyfluoroaikane or from 2 to5 carbon atoms having at least two fluorine atoms on at least one carbonatom and at least one hydrogen atom on an adjaoent carbon atom, that is,on a carbon atom adjacent to a carbon atom carrying at least twofluorine atoms. Differences have been observed in the effect ofpyrolysis on saturated and unsaturated compounds.

In the pyrolysis of the polyiluoroalkanes, the reaction appears toinvolve primarily an intramolecular dehydrofluorination, wherein bothelements of the hydrogen fluoride are obtained from the same molecule,to produce fluoro-olefines which have a tendency to polymerize. Forexample, the pyrolysis of cmcr's produces primarily CH2=CF and CHPC FPOFI-UH:

Although for the production of particular compounds the reaction will becarried out under well-controlled conditions of time, temperature andpressure, complex mixtures of compounds of various molecular weights canbe produced by subjecting the compounds to pyroiytic conditions forextended periods of time. Pressures may also be used to vary theresults, although for the purposes of economy and safety each particularreaction should he carried out with the lowest pressure consistent withoptimum results. For example, pressures of four atmospheres absolutehave been found satisfactory in many cases. In general, operations maybe carried out at pressures between 0.1 and 10 atmospheres absolute, butother pressures are useful and may be employed when an increase ineiliciency will result.

This is a pyroiytic process. The disintegration and integration areproduced essentially by heat. It is, therefore, important to select atemperature which will emciently produce the reaction. The temperatureshould be selected to give optimum production of the desired product. Wehave found that excellent pyrolytic results have been produced attemperatures between 600 and 1000" C., but that particular substanceshave been pyrolyzed at temperatures as low as 400' C. and above 1000" C.under appropriate conditions of time and pressure. Electrical heating isefllcient, but any method of heating may be applied. The temperatureswhich are used must also be chosen in view of the materials that composethe reaction apparatus.

The time of exposure of the reactants to the pyrolytic conditions is amatter of considerable importance where a particular product is desired.Extending the period of exposure frequently produces compounds ofincreased molecular weight.

In general, the pyrolysis proceeds to the integration of new fiuorohydrocarbons eflloiently in the absence of catalysts. Heavy metalhalides, such as those of iron, copper and nickel, and halides of thealkaline earth metals, such as Bach and CaCh may be used.

The process is preferably carried out continuously by passing theconvertible material through a tube heated to a pyrolytically effectivetemperamm. The tube should be composed of a material which is inert tothe reaction and the reaction products. Carbon and the noble metals aresumcientiy inert and have proved to be satisfactory materials for theconstruction of reaction chambers. The chamber need not be whollycomposed of the inert material, but may be lined with it. Reactionchambers containing a platinum lining are particularly satisfactory. Theprocess may be carried out in batches rather than continuously, butcontinuity is preferred.

The following examples have been carried out and have been selected forinclusion in this specincatlon because they show a number of thecomounds which have been successfully pyrolyzed, and a number of classesthereof, and a variety of reaction conditions. The applicants presentthese examples, not as constituting any limitation of the work which hasactually been done, but as sufliciently representative to enable personsskilled in the art to practice the invention, In these examples theterms "conversion" and "amount converted include the assumption that thedisappearance of one mol of the primary organic material resulted in theliberation of one mol of halogen acid. This assumption is warranted bythe close agreement between the figures for conversion obtained by acidanalysis and the actual primary material which disappeared. Unlessotherwise noted, the examples were carried out at a pressure of aboutone atmosphere. The temperatures of the pyrolyses were measured withathermocouple which was placed in contact with the outer surface of thereaction tube near the center of the heated zone, so that the trueaverage temperature of the gases in the tube may have been somewhatlower than the values given.

Example I CHaCFa was passed through a nickel jacketed Example II 08:01:was passed through a platinum-lined Inconel jacketed nickel tube, 19mm. 1. D. x 60" long, at a rate of about 24 g. per hour at a tubetemperature maintained at about 820 C. The reaction products were washedwith water, dried and condensed in receivers cooled in acarboniccacetone, bath followed by a receiver cooled in liquid nitrogen.The compounds, obtained in this pyrolysis, were the same as thoseobtained in Example I. Material, condensed in the liquid nitrogenreceiver, was isolated and identified as CH2=CF:, boiling at -82 C. andconstituted part of th CH2=CF2 formed. Some CH1=CF2 was present in themixture condensed in the carbonice-acetone receivers. A fraction of thematerial condensed in the carbonice-acetone receivers boiled at 50 C.and was identified as tetrafluorocyclobutane having the formula CHr-CFr-CFr-CIL Example III CHr-C Fr-C F's-UH:

Example IV During a period of 6 hours, a total of parts of1,1-difluoroethane was passed through a silverlined steel tube 0.6 inch1 D., and 54 inches long heated to 690-764 C. in a 3 ft. electricfurnace. The off-gases were scrubbed with water, passed over soda andlime, dried over calcium chloride and the product was collected in asolid carbon dioxide-acetone cooled trap, backed up with a liquidnitrogen cooled trap. At the conclusion of the pyrolysis, the waterscrubber gave a positive test for fluorine and was acidic. Titrationindicated that 6.4 parts of hydrogen fluoride had been formed in thereaction. Distillation of the organic product collected in the solidcarbon dioxide-acetone cooled trap gave the following results:

Parts Fraction 1--Boiling point 69 to 27 C. 4 Fraction 2-Boiling point-27 to 17" C.-- 51 Fraction 3--Boiiing point 17 to -11 C. 9

The lowest boiling fraction contained crude vinyl fluoride which boilsat '72 C. when rigorously refined.

Example V moval of acetylene with aqueous silver nitrate solution, thegaseous product was condensed and collected in a solid carbondioxide-acetone cooled trap. Distillation of the trapped material gave48.6 parts of vinyl fluoride (B. P. 70' to -62 0.), 24.4 parts ofintermediate material (B. P.

l 8,480,500 8 6 -62' to 30' C., a mixture of vinyl fluoride and and isshown not to be cyclic since it reacts with unreacted LI-diiiuoroethaneland 82 parts permanganate and because it boils 12' higher unchangedl,i-difluoroethane. This represents than the known cyclic compound. ayield of 71 96. and a conversion of 40% based on lump w" thei,l-diiluoroethane charged a w CEaCHaCI-l'i was pyrolysed in aplatinum-lined tube similar to that described in Example vn.2,2-diiiuorobutane -('30 parts) was passed At a tube temperature of(ISO-850 0., about 35 g. through an Inconel'tube heated to 660" 1- 8 C.4 of organic material was fed through the tube in over' a period of 45minutes, corresponding to a m the course of two hours. The reactionproducts contact time of 1.6 seconds. The pyrolysis prodwere washed withwater, dried over calcium sulucts were passed over soda and lime to.remove fate and condensed in receivers cooled in a carhydrogen fluorideand were condensed in a carbonice-acetone bath, followed by a tailingreceiver bon dioxide ice-acetone cooled trap. Distillation pooled inliquid nitrogen. Analysis of the wash of the trapped material gave llparts of 2-fluorowater showed about 3g. of HF. butene boiling at C. to2'! C. and having a re- About g. of material was condensed in thefractive indexof an", 1.8302. The residue, carbonice-acetone trap andabout 8 g. of maprising 20 parts, had a refractive index of un tei'ialinthe liquid ni ro n trap. These two coni.3220 indicating it wasunchanged SJ-diiluorodensates wereplaced in the Podbielnial: still andbutane. 7 2o fractionally distilled. The following fractions The2-iiuorobutene was converted to the iiuorowere identified: dibromobutaneby reaction with bromine in carbon tetrachloride. The followinganalytical re- 7 Molecular Weight suits on the dibromide (B. P. IMP-162'C.) were Boiling Range, '0. com, obtained. 2; Calculated Found 1 MolarPee cm. Per cm l -m to -ioa CHFCHI 2a 2.4 m 2 -ss or on e4 use R m a 3mm4st: 12.-- en's Loni it 46.2

4 -D to 2z. CF1=CHOH|.-... 78 81. Oelc'd. ihr O Hvl'Bn m1: g 1 e7 3 5 l6to l 0FiCHrCH|. 06 W. s Ionnd secs aaaa i zlAssnhnries x m ue fgl;compound of this type gives a w Example 'l g main oonstl l nt I; dieEroduct was argon-0m. H(C1"2)eFWa8 passed throughaplatinum-lined The r np odu m y be Wa h d with Inconel jacketed nickel tube 8 1, D, g 15" long85 water or alkaline solution to remove acid constitat a rate oi about19-20 g. per hour. The surface vents be'fore c e sa i n a ana ysis.altemperature was maintained at about ear-850C. thoush t s is n t n cssa In s cas s. it is over an estimated length of 8" by electricalheatadvantageous Separate 081158111 desired 00ming. The organic materialwas fed liquid phase P01163138 before M removallnto the pyrolysis tubethrough a calibrated The particular advantage of the invention ispipette. The eiiiuent reaction products were that a pvro tic p ss as n dvered for washed with water. dried and condensed in rethe P c ion 01 n woomp unds and for the eeivers, cooled in carbonice-acetone, followed by815018111; Pro c on of Old compounds. a tailing receiver cooled inliquid nitrogemi which is characterized y ts p ic ty a d the About 25 g.of condensate was collected in the with which it may be DPeTEtEd- Theinvencarboniee-acetone trap with 1.35 g. of material in Provides ineminent method 01 D 8 the liquid nitrogen receiver. An additional 1.5 g.013M110 compounds ntai ing fluorine. particof "high boilersunlndentliled) were separated mmrmated defines- These compound! from twash waten An analysis of the wash 0 have uses in themselves, such asfor refrigerwater showed the presence 01 Q9 f nn The 5 ants,anaesthetics, and solvents and are useful as liquid nitrogen condensatewas found to be can intermediates for the r duction of alcohol, esandhadabginng point of 7 e. um molecular ters, halides, and alkylderivatives. A particuweight of 99 (calculated for .CaFi! molecularadvantage of the lnventmn is that the P is The carbonlce acetone onden655 is most emcient for the production 01 the Valsate was distilled onthe Podbielnial: column and able compounds Cm and found to contain the fllowi actions: which are intermediates of wide utility, particularly forrefrigerants and plastics. The invention is also useiul for thesynthesis of compounds 30mm an C and m having more carbon atoms than thecompound cumin round, pyrolyzed, and for the extension of carbon chains.d'lshe processi involves the pyrolysis of compoun of both lght and heavymolecular -2-5IIIIIIIII fldeiiuheliIII weight. The pyrolysis has beencarried out in 4 :gflg jg;- :33 both a continuous and a step-wisemanner, and

s -sa to -s1. ..de..- ""ico a large variety of conditions has beenemployed,

" I 83%}??{1 m 1% so that it is beyond question that the process is a +7-J. our, not an of general application.

As many apparently widely diiferent embodi- Assumes 1 v=nr which for acompound oi this type gives a ments of this invention may be madewithout dea 4% high parting from the spirit and scope thereof, it is toThe largest fraction was fraction (8). The oleiinio' b und rstood thatwe do not limit ourselves to nature of fractions (1), (6), (7) and (8)was demth specific embodiments thereof except as d onstrated by the factthat they reduced aqueousfined in the appended claims.

alcoholic KMnO4 solution. Fraction (8) most We claim:

probably has the structure OWE- 01': l. The process which comprisespyrolysing at on an adjacent carbon atom, an carbons carryin: a singlefluorine atom being adjacent a carbon carrying at least 2 fluorineatoms.

2. The process which comprises pyroiyzin: a

trifluoroethanc consisting of the elements. bonfl hydrogen and fluorineat a temperature'o! from about 600 C. to about 1000' C.

8. The process which comprises CHJCFB at a temperature of from about 600C, toabout 1000' C.-

FREDERICK B. DOWNING., ANTHONY 1 BENNING. ROBERT 0. mm.

The toliowin references are of record in flle or this intent:

UNITED STATES PATENTS Number Name Date 1. 9.810 mmet ai. Jan. s, 1935,878,859 s m et a1. June 19. 1945 Mugdan et a! June 28, 1945 a 0am oneBenderens, -"Buli. Soc. Chim. de France, 4th

oer-intro]. 8, page: 823-829 (1903).

Gflman. Orunic chemifliry" (2nd ed.-. 1943), vol. 1, page: 56-057.

